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I'm looking at potentially replacing our old natural gas tanked water heater, we are having supply issues, keeping up with all the people showering in the house and not being able to run any appliances that need hot water at the same time. I know it probably won't pay itself off, but I am a Direct Buy member and can get one for a pretty decent price, and am fairly handy, and definitely think I can handle the install on my own. I just have a few questions about what kind, what size, etc.

I have a 2 story 1800+/- sq ft house with 2.5 baths, the 2 upstairs have the shower/tubs, the one downstairs is just the .5, and the water heater is currently located in the garage, which is where I would most likely mount the new one as well. I have read up on some of the differences between condensing and non condensing units, but have a question about that as well; if I buy a condensing unit(about $250-300 more than a non) can I just use my existing exhaust piping or would I need to put new exhaust piping in? If I can use existing and we're looking at around $30 a foot for piping, paying the extra for a condensing unit would be worth it, if not, I would probably go the other way for cost reasons. What size unit would I need for a house my size? I'm hesitant to talk to local plumbers as I will ultimately not be using them for anything, and was hoping I could get some answers here. I've also seen on some DIY shows, some pretty intense looking manifold setups for tankless water heaters, but have never heard why they do these, and am not 100% sure it's something I need or want. I know I can just hook into the existing lines, but what is the benefit or purpose of these manifolds?

Thanks in advance for any guidance anyone can give!
 

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There are many problems associated with tankless systems....one of which is poor distribution as I heard from an installer, who called into a radio show promoting them, a few years back. I do not have any direct experience but, I would think a manifold is a way to size the distribution to overcome these problems..I also read ( I think in a Canadian Government energy study) where the payback for the tankless is so long that sticking with tank type costs the same in the long term but it is easier on the wallet short term...hopefully more comments will be provided for your consideration.
 

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Not A Licensed Pro
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I looked into tankless a while back... resolved to one day only put a point-of-use or tankless for the kitchen since its such a long run from the HWH, everything else is a fairly short run.

before replacing it, consider getting by with what you have and put off replacing the HWH until it breaks down...

1. do you have low flow shower heads? I'm not talking the standard 2.5GPM ones, but 1.75GPM ones. money not wasted since you'll save money if you replace the tank or not. Three 10 minute showers will drop from 75 gallons to 53 gallons. Also my shower heads have a switch where I can shut off the spray on/off without screwing up the cold/hot mixture and it's quick and easy to operate and you don't have to dodge the (wasted) spray while soaping up.

2. can the temperature of your water heater be turned up to increase its total heat capacity?

venting... you may find yourself required by code to upgrade to 3 or 5" stainless steel double vents ... from the consumption needs you state, most likely the 5" vent.
 

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Master Plumber
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I would recommend having pro install it, if only for the simple reason of the warranty, few moths back had a homeowner install his own apart from multiple safety and code violations he use a little too much pipe dope and damaged the flow switch, which voided the warranty which left him without hot water for a few days which cost him for labor and parts plus expedited shipping cost. and now has a unit that has no warranty because he did not use a qualified installer.
 

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flipping slumlord
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I'm looking at potentially replacing our old natural gas tanked water heater, we are having supply issues, keeping up with all the people showering in the house and not being able to run any appliances that need hot water at the same time.
How many people?
Is everyone on the same basic use/demand schedule?

Thanks in advance for any guidance anyone can give!
I'd buy a second standard WH before I'd buy a tankless.
 

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Two schools of thought here: 1. Tankless heaters are the best thing ever invented. 2. Tankless heaters are the worst thing ever invented. There seems to be no middle ground. We have a gas tankless and love it. I installed it myself when we built the house. It is in the attic, mounted on an outside wall, so the length of that expensive vent pipe is very short as it is horizontally vented through the wall.

I don't understand the earlier comment about poor distribution with a tankless unit. That's a function of piping layout, not how the water is heated. But probably the most important thing about tankless units is getting one that's properly sized for your water usage requirements. Another important thing to know is that they do not do well if you have hard water - it will kill them in short order.

How is that Direct Buy thing working out for you? We bought a membership about five years ago because were were starting to build our house and would be buying appliances, cabinets, countertops, etc., etc. Turned out to be a waste of money for us. Even though I am not a professional contractor, I was able to get contractor pricing from several local places so didn't have to deal with the hassle of long waits for things and then having to arrange delivery or pick them up myself. We finally just let the membership lapse.
 

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Doin' work
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Discussion Starter #7
md2lgyk said:
Two schools of thought here: 1. Tankless heaters are the best thing ever invented. 2. Tankless heaters are the worst thing ever invented. There seems to be no middle ground. We have a gas tankless and love it. I installed it myself when we built the house. It is in the attic, mounted on an outside wall, so the length of that expensive vent pipe is very short as it is horizontally vented through the wall.

I don't understand the earlier comment about poor distribution with a tankless unit. That's a function of piping layout, not how the water is heated. But probably the most important thing about tankless units is getting one that's properly sized for your water usage requirements. Another important thing to know is that they do not do well if you have hard water - it will kill them in short order.
That seems to be the feeling I get when I talk about them. Someone recommended putting a second standard water heater in before a tankless. And while I'm not an expert, that seems like it would be terribly inefficient. There are currently only 3 of us, but if all of us shower within an hour, which does happen quite often, the third person is getting a cold shower. And I'm not willing to tell my wife to take a 2 minute submarine shower. Both showers do have low flow heads, but it seems that third person always gets cold water, or if the washer or dish washer is running the first person will barely make it out warm.

I guess my big question is what size do I need?

How is that Direct Buy thing working out for you? We bought a membership about five years ago because were were starting to build our house and would be buying appliances, cabinets, countertops, etc., etc. Turned out to be a waste of money for us. Even though I am not a professional contractor, I was able to get contractor pricing from several local places so didn't have to deal with the hassle of long waits for things and then having to arrange delivery or pick them up myself. We finally just let the membership lapse.
We love our direct buy membership. So far we haven't waited more than 2-3 weeks for anything, and have been able to get home delivery on almost everything we've ordered to date. We found it's great for Christmas, or if we know we'll be headed to a house warming or something like that we can order nice housewares outrageously cheap. I got both of my sisters Lennox vases for Christmas this year, retail on both were around the $150 range, which we saw at bed bath and beyond, and we paid around $25 for each of them, and my sisters thought they got expensive Lennox crystal lol. I wouldn't hesitate to become a member again, but we use it, if you aren't going to use it, it's a waste. Also the website is fantastic definitely beats going to the club to order most things, our club is only about 50 miles but it's OC traffic and its nice not dealing with that.
 

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Discussion Starter #9
TarheelTerp said:
Change that pattern of use and you don't have to make any other changes.
When 3 people wake up at 6 and have to be out the door by 7:30, that's easier said than done.
 

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I put a Rinnai rc80in in our house in September. It has been excellent so far. It's a condensing unit rated 8gpm by Rinnai but looking at the flow chart for a more realistic number it's 5gpm at 60F rise which is around average for us here. That's plenty for 2 showers with full hot water running.

We've never run out of hot water. We have 3 kids from 7-11 and they take their showers right in a row with maybe 2-3 minutes between them, so the water runs almost non-stop for probably 40 minutes plus we can run dishes during that as well and never have a problem. Normal 50 gallon tanks can't handle that here with the 47F cold water supply temp in February, just not possible with only 40k BTU capacity.

The Rinnai uses a combined intake/exhaust vent pipe setup, there are considerations with slope/distance/etc, but for my setup it went straight through the wall the unit is mounted on.

$$ payback wasn't a concern here, I wanted something that provided hot water without us having to worry about 'usage patterns' or anything. One benefit was I was able to put it on an exterior wall between the 2 bathrooms so the time to get hot water at the tap is minimal, maybe 20 seconds. If I had done a normal tank, it couldn't be located where it is and would have increased that time.
 

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The websites for companies selling tankless heaters have charts and such to help you figure out what size you need. I don't think oversized is a problem; it's undersized that will get you lukewarm water at times.

You mentioned submarine showers. Did you actually serve on a sub? I did, back in the 60s and 70s. SSBN-654.
 

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Discussion Starter #15
TarheelTerp said:
Right. No one else has ever had this issue come up before.

Figure it out.
I did wise guy, I'm getting a tankless water heater. I just need some details on the one that is best for me. If you can't contribute anything useful, there's whole wide world of interwebz for you to troll up. I didn't ask for an alternative shower schedule, or your opinion on how I should handle my home life, I asked for knowledge about tankless water heaters.
 

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Discussion Starter #16
md2lgyk said:
The websites for companies selling tankless heaters have charts and such to help you figure out what size you need. I don't think oversized is a problem; it's undersized that will get you lukewarm water at times.

You mentioned submarine showers. Did you actually serve on a sub? I did, back in the 60s and 70s. SSBN-654.
No, I never served on a sub, but in searching this forum for info on tankless water heaters the sub shower came up in just about every thread. Thanks for your service btw.
 

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JOATMON
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aricus......md2 summed it up pretty good...

What size tank do you have now? I have a 50 gal and we have never had an issue.

I'm in the same basic area and I've done a lot of research into the same subject. Some of the conclusions I've come to...

If you have an electric water heater....tankless is a good way to go over getting another electric tank heater.

A gas tankless has a much longer payback....by my estimates...about the time it's reached the end of it's life...your just starting to get a payback....except for the following.

If you use a big slug of hot water for just a short period of time...say in the morning....then basically, there is no hot water demand for several hours....then the payback starts to be there. Or, if you have more hot water demand than a tank heater can keep up with....

If you use hot water all day long like we do, a tankless does not have the payback.....I can buy 2 gas tank heaters for the cost of one tankless...and since they have a 12 year warranty (which means they last about 20 years)....the payback is not there.

If you go tankless gas....you will most likely need to upsize your gas supply....and I think your vent needs to be larger.....
 

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I just ran some heat balance numbers. This is interesting.

On a normal 50 gallon tank with a 40k btu/hr burner, with 120F outlet temp and 50F inlet, if you take a 30 minute shower (3 kids in a row or maybe 2 adults taking long ones) with a 2.5gpm flowrate, you'll have 90F water in the tank at the end of 30 minutes. I didn't take into account any heat from the tank material itself, so it would be higher because there is quite a bit of thermal mass there.
 

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aricus......md2 summed it up pretty good...

What size tank do you have now? I have a 50 gal and we have never had an issue.

I'm in the same basic area and I've done a lot of research into the same subject. Some of the conclusions I've come to...

If you have an electric water heater....tankless is a good way to go over getting another electric tank heater.

A gas tankless has a much longer payback....by my estimates...about the time it's reached the end of it's life...your just starting to get a payback....except for the following.

If you use a big slug of hot water for just a short period of time...say in the morning....then basically, there is no hot water demand for several hours....then the payback starts to be there. Or, if you have more hot water demand than a tank heater can keep up with....

If you use hot water all day long like we do, a tankless does not have the payback.....I can buy 2 gas tank heaters for the cost of one tankless...and since they have a 12 year warranty (which means they last about 20 years)....the payback is not there.

If you go tankless gas....you will most likely need to upsize your gas supply....and I think your vent needs to be larger.....
Excellent post. For our situation, I was lucky that the gas line was large enough already, I only needed a short vent kit to go through the wall, and I picked up a brand new Rinnai condensing for $900 shipped. Total cost for everything ended up being around $1200. I may eventually break even compared to a gas tank, but paying a little extra for the benefits we get out of it is worth it.
 

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No, I never served on a sub, but in searching this forum for info on tankless water heaters the sub shower came up in just about every thread. Thanks for your service btw.
Thank you for that. While I did serve 8 years in the Navy, I eventually ended up retiring from the Air Force. Given the pension and medical benefits, it's one of the smartest things I've ever done.
 
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